Analytical information
The CS16 column has a stationary phase containing negatively charged carboxylic acid functional groups, and uses dilute methylsulfonic acid as an eluant. The eluant is made by the eluant generator, usually using a concentration gradient program that gradually increases the eluant concentration as the run progresses. This system can separate a wide variety of cations.
The procedure here is for eight inorganic anions in natural waters: Li, Na, NH4+, K, Mg, Ca, and Sr. It turns out that NH4+ is quite common, in very low concentrations, in many natural waters. Ba and Mn2+ can also be analyzed. Ba is usually at or below the detection limit in most waters, so analyzing it is usually a waste of time especially since Ba is the last component to elute and so it increases analysis time considerably (50%). Mn2+ occurs only in reducing waters. Its peak lies in the saddle between Mg and Ca and so is difficult to quantify in high Mg samples. Ba can be analyzed reliably if its concentration is >0.05 ppm, and and Mn can be analyzed if the Ca/Mn and Mg/Mn ratios are <20 or so. Ba and Mn2+ can easily be added to the method and to standards.
Sample preparation
All samples should be kept refrigerated and in the dark until they are analyzed, which should be done as quickly as possible. Samples must be free of high molecular weight organics (tannins, etc.) or particulates. If samples precipitate anything, such as calcite, prior to analysis that might have a chemical component you want to analyze, you must put the precipitate back into solution before analysis. In doing so, do not to make the samples strongly acidic or alkaline.
All natural samples need to be filtered for particulates through a ≤0.45 μm filter, and some must be filtered for high-molecular weight organics. These will damage the column, and particulate damage is irreversible. Refer to the following table:
| Sample content | 0.2 μm particle filter $1.50 each | OnGuard P* filter $3.15 each |
| Normal, colorless, dilute samples. | Yes | No |
| Brown samples having dissolved tannins or other high molecular weight organic compounds. | Yes | Yes |
| * Removes high molecular weight organics. | ||
Follow the instructions with the filters. Filters can be stacked on the end of the syringe and filtered in one step, with the particulate filter being the last. The filters are expensive so do not waste them.
Standard preparation
In general, standards should be similar in composition to the samples being analyzed. Since samples vary enormously, you may want to start with a generally useful standard. For this, dilute the following stock solutions in a 100 ml volumetric flask.
| Ion | Stock concentration, ppm | ml used | Standard/1, ppm |
| Li+ | 1000 | 0.05 | 0.5 |
| Na+ | 1000 | 10 | 100 |
| NH4+ | 1000 | 0.1 | 1 |
| K+ | 1000 | 0.5 | 5 |
| Mg2+ | 1000 | 5 | 50 |
| Ca2+ | 1000 | 10 | 100 |
| Sr2+ | 1000 | 0.2 | 2 |
Transfer Standard/1 to a clean 125 ml plastic bottle. Transfer appropriate numbers of 5.5 ml aliquots of DI water and Standard/1 to four other bottles. The numbers of 5.5 ml aliquots are as follows:
| Standard/1 | Standard/2 | Standard/5 | Standard/10 | Standard/20 | |
| 5.5 ml aliquots of DI water | - | 5 | 8 | 9 | 9 |
| 5.5 ml aliquots of Standard/1 | - | 5 | 2 | 1 | 1 from Standard/2 |
| Ion | Resulting concentrations, ppm | ||||
| Li+ | 0.5 | 0.25 | 0.1 | 0.05 | 0.025 |
| Na+ | 100 | 50 | 20 | 10 | 5 |
| NH4+ | 1 | 0.5 | 0.2 | 0.1 | 0.05 |
| K+ | 5 | 2.5 | 1 | 0.5 | 0.25 |
| Mg2+ | 50 | 25 | 10 | 5 | 2.5 |
| Ca2+ | 100 | 50 | 20 | 10 | 5 |
| Sr2+ | 2 | 1 | 0.4 | 0.2 | 0.1 |
The result will be 56 ml of Standard/1, 49.5 ml of Standard/2, and 55 ml of the others. Pour ~3 ml of each standard into Dionex autosampler tubes, and press a black filter cap into the top of each using the filter cap tool. You should run standards at least at the beginning of the run and perhaps also within the run. Alternatively, you can periodically run a check sample and do corrections off line.
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